This invention relates to composite bearings, and, more particularly, to an improved composite ball and socket bearing having a replaceable outer socket.
Ball and socket bearings are designed for applications where both misaligning and oscillatory motions are present. These bearings are sometimes referred to as self-aligning bearings, and typically comprise a bearing with a spherical outer diameter, referred to as the ball, mounted within an opening, or the socket, of a housing, thus forming the ball and socket bearing. For convenient reference, the term "socket" will be used to refer to the socket and its housing. The socket comprises a concave internal surface or raceway that is integral with the housing. The socket internal raceway and the outer spherical diameter of the ball must have a predetermined close tolerance fit to assure consistent bearing performance and long life.
The close tolerance fit between the ball outer surface and the socket internal raceway can be assured by permanently mounting the spherical ball in the internal raceway of the socket, thus producing a unitary ball and socket bearing which can be tested for the desired predetermined close tolerance fit as a final step before marketing. Many such bearings are known having metallic sockets permanently forged or otherwise formed onto metallic balls to form a unitary ball and socket bearing. Such unitary ball and socket bearings are difficult and expensive to manufacture, and there is always a risk of the steps of forming the final assembly causing damage to either the ball outer surface or the socket internal raceway, which would adversely affect the close tolerance fit of the bearing interface. Further with this design the ball alone is not replaceable and therefor when replacement is required the entire unitary ball and socket bearing must be replaced which means that it is not practical to permanently mount the metallic socket. Such a combination of a ball and a permanently affixed socket will be referred to as a replaceable bearing subassembly because it is usually designed to be replaceably mounted as a unit within a separate outer housing or pillow block, which can be permanently mounted.
It is often desirable, however, that either the ball or the socket be individually replaceable as they wear, or as the application requirements for the bearing change, and so the ball is also often designed to be removable from the socket. This type of bearing will be referred to as a removable ball and socket bearing. Such a removable ball and socket bearing is shown in U.S. Pat. No. 3,116,539, J. R. Evans et al. issued Jan. 7, 1964, which discloses a socket having insertion slots diametrically spaced apart on one side of the socket, permitting insertion of the ball into the internal socket raceway. The ball is inserted sideways through the insertion slots and turned ninety degrees to seat the spherical outer diameter or surface of the ball within the socket raceway, making the ball easily removable from the socket. The socket may then be permanently mounted and the ball replaced as necessary, or, conversely the socket may be temporarily mounted so that the ball or the socket, but not necessarily both, can be replaced.
Generally such metallic sockets are produced by swaging or otherwise forming a malleable metallic socket to conform to the surface of the metal ball. The problem with such processing steps is that the socket may be weakened, or the outer surface of the ball or the raceway of the socket damaged, which will have adverse consequence on the wear rate for the bearing. In addition, the insertion slots must be machined or formed in the socket. The insertion slots reduce the surface area of the concave internal raceway, and must be carefully generated in manufacture to avoid producing irregularities in the internal raceway surface which might lead to increased wear.
A different type of replaceable bearing subassembly is disclosed in U.S. Pat. Nos. 3,700,295 and 3,974,009, both issued to Butzow et al., on Oct. 24, 1972 and Aug. 10, 1976, respectively. This replaceable bearing subassembly comprises a resin-impregnated filament-wound annular socket having a concave internal raceway and a corrosion resistant spherical steel ball which will be referred to as a composite replaceable bearing subassembly. This combination provides a composite, lightweight, corrosion-resistant replaceable bearing subassembly. This composite replaceable bearing subassembly also has a self-lubricating surface of a low friction material, such as a woven Teflon fabric, on the internal raceway of the annular socket, and is produced by a process comprising applying the fabric over the spherical steel bearing assembled on a mandrel and then building up the body of the socket member over the fabric by repeatedly winding resin-impregnated fiberglass filaments about the fabric. The resulting resinous body is subsequently cured to harden the resin. The internal raceway surface thus comprises a layer of Teflon fabric, which forms a low friction bearing surface against the outer surface of the steel ball. This process of producing a composite replaceable bearing subassembly provides the desired close tolerance fit between the outer spherical diameter of the ball and the socket internal raceway, and avoids the disadvantages of the difficult forming or forging steps previously discussed. With a fiberglass socket formed over a steel ball in this fashion, a composite replaceable bearing subassembly is produced which is lighter, less expensive and easier to manufacture than a replaceable bearing subassembly having a metallic socket member formed over a metallic ball.
A lightweight composite replaceable bearing subassembly having a fiberglass socket is strong relative to other lightweight, non-metallic materials. However, if a composite replaceable bearing subassembly is to be provided with insertion slots to make either the ball or socket replaceable, the insertion slots must still be machined into the socket, such as by grinding or milling. Because a fiberglass socket is not malleable such a socket cannot be formed over the ball by conventional forming or swaging methods. Slots must be cut into the body of a fiberglass socket member with great care to avoid damaging the socket, such as by stress fractures or chipping, and also to avoid marring the surface of the internal raceway. Thus the process for producing a replaceable fiberglass socket member of a ball and socket bearing is time consuming, labor intensive and results in more waste, raising the cost of producing such a socket member.
If the internal raceway of the bearing outer socket is lined with a low friction Teflon fabric, machining of the insertion slots will create serious disadvantages. Machining or cutting away low friction fabric from the internal raceway to create the insertion slots, which results in part of the raceway being not covered by low friction fabric and also results in frayed fabric on the raceway surface, decreases the life of the bearing. The insertion slots constitute high friction areas in the raceway which decrease the frictionless nature of that surface.
Therefore, in spite of extensive development in the bearing art, a need exists for a simple, low cost process for producing a composite removable ball and socket bearing wherein insertion slots are formed in the socket during manufacture to eliminate the need for machining or cutting into the socket after it has been formed and, if desired, for lining the socket raceway and insertion slots with a self-lubricating material. A need also exists for a removable ball and socket bearing having both the raceway and the insertion slots lined with a self-lubricating material.